Thin film, method for manufacturing thin film, and electronic component

ABSTRACT

A method for manufacturing a thin film is performed such that the internal stress is controlled while the preferred orientation property is maintained at a high value. An AlN piezoelectric thin film is formed on a substrate by a sputtering method using a mixed gas including Ar and nitrogen, wherein the mixed gas has a nitrogen flow rate ratio, that is, nitrogen flow rate relative to the sum of the Ar flow rate and the nitrogen flow rate, of about 10% to about 75%.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a thin film, a method formanufacturing the thin film, and an electronic component. Moreparticularly, the present invention relates to a thin film, for example,a piezoelectric material thin film, a dielectric material thin film, anda magnetic material thin film, or other suitable thin film, used for anelectronic component, for example, a piezoelectric thin film resonator,a filter, sensor, and an actuator or other suitable device.

[0003] 2. Description of the Related Art

[0004] Since a resonant frequency of a piezoelectric resonator using athickness longitudinal vibration of a piezoelectric substrate isinversely proportional to the thickness of the piezoelectric substrate,in the superhigh frequency regions, the piezoelectric substrate must beprocessed extensively to be very thin. Regarding the decrease in thethickness of the piezoelectric substrate itself, however, in thefundamental mode, several 100 MHz have been believed to be the practicallimit of the high frequency due to the mechanical strength andrestrictions in the handling thereof.

[0005] In order to solve the aforementioned problems, diaphragm typepiezoelectric thin film resonators have been suggested, and have beenused for filters and resonators. FIG. 5 is a sectional schematic diagramof an example of a conventional piezoelectric thin film resonator. Thepiezoelectric thin film resonator 1 as shown in FIG. 5 includes a Sisubstrate 2. A thin film support member 3 having a thickness of severalμm or less is formed on the substrate 2 by a partial etching from thereverse surface using a micromachining method. An AlN piezoelectric thinfilm 5 is provided on the thin film support member 3 as a piezoelectricmaterial thin film including a lower layer electrode 4 a and an upperlayer electrode 4 b on both major surfaces as a pair of excitationelectrodes. The thin film support member 3 and peripheral portionsthereof thereby define a diaphragm 6. In the piezoelectric thin filmresonator 1 as shown in FIG. 5, the thin film support member 3 can beformed to be thin using the micromachining technique, and the AlNpiezoelectric thin film 5 can be also formed to be thin by thesputtering, or other suitable process, so that the high frequencycharacteristics may be extended to several 100 MHz to several 1,000 MHz.

[0006] In order to produce resonance characteristics that are superiorin the temperature characteristics of the resonant frequency and in theantiresonance characteristics, a piezoelectric thin film resonator asshown in FIG. 6 has been suggested. FIG. 6 is a sectional schematicdiagram of another example of a conventional piezoelectric thin filmresonator. When the piezoelectric thin film resonator 7 as shown in FIG.6 is compared with the piezoelectric thin film resonator 1 as shown inFIG. 5, a thin film 8 made of SiO₂, Si₃N₄, Al₂O₃, or ZnO, is formed asthe upper layer of the Si substrate 2.

[0007] In order to realize the piezoelectric thin film resonators 1 and7 as shown in FIG. 5 and FIG. 6, the stress of the entire device must becontrolled so as not to destroy the diaphragm 6. Since the thin film ofSiO₂ has strong compressibility, the thin films of Si₃N₄ and Al₂O₃ havea strong tensile property, and so forth, the internal stress of the AlNpiezoelectric thin film 5 must be controlled.

[0008] It is said that in order that excellent piezoelectricity to beachieved in the AlN piezoelectric thin film, the C axis is preferablyoriented in the direction that is perpendicular to the substrate, andthe half-width of the rocking curve is preferably small, as describedin, for example, “Acoustic Wave Technology Handbook” written by theJapan Society for the Promotion of Science, 150th Committee on AcousticWave Technology issued by Ohmsha, Ltd., 1991. In general, in the case inwhich the AlN piezoelectric thin film is formed by the sputteringmethod, an excellent C axis preferred orientation film is produced at alow gas pressure region, that is, at a film generating a pressure of 0.6Pa or less, as described in, for example, J. Mater. Res., Vol. 12, No.7, p. 1850 (1997) by A. Rodriguetz-Navarro, W. Otano-Rivera, J. M.Garcia-Ruiz, R. Messier, and L. J. Pilione. On the other hand, since thepeening effect is strong at the low gas pressure region, the formed AlNpiezoelectric thin film has strong compressibility. Therefore, theinternal stress of the AlN piezoelectric thin film has previously beencontrolled with the gas pressure during the film formation.

[0009] When the gas pressure during the film formation is increased,however, the preferred orientation property of the AlN piezoelectricthin film is reduced, and accompanying this, the resonancecharacteristic is also reduced. As a consequence, the internal stress ofthe AlN piezoelectric thin film controlled by the gas pressure and thepreferred orientation property have a t rade-off relationship, so thatcontrolling the internal stress while keeping the preferred orientationproperty high was not possible.

SUMMARY OF THE INVENTION

[0010] In order to overcome the problems described above, preferredembodiments of the present invention provide a thin film and method ofmanufacturing the same, in which the internal stress is controlled whilethe preferred orientation property is kept high.

[0011] Also, other preferred embodiments of the present inventionprovide an electronic component including a thin film in which theinternal stress is controlled while the preferred orientation propertyis kept high.

[0012] According to a preferred embodiment of the present invention, athin film primarily including AlN formed on a surface of a substrate isprovided, in which the crystallinity is the C axis preferredorientation, the half-width of a rocking curve is about 1.4° to about1.6°, and an internal stress can be controlled within the range ofapproximately ±1 GPa.

[0013] According to another preferred embodiment of the presentinvention, a method for manufacturing a thin film includes the steps offorming a thin film according to various preferred embodiments of thepresent invention by a sputtering method using a mixed gas including Arand nitrogen, wherein the mixed gas has a nitrogen flow rate ratio, thatis, a nitrogen flow rate relative to an Ar flow rate and the nitrogenflow rate, of about 10% to about 75%.

[0014] According to another preferred embodiment of the presentinvention, an electronic component includes a thin film according topreferred embodiments of the present invention.

[0015] Regarding preferred embodiments of the present invention, bycontrolling the nitrogen flow rate ratio of the mixed gas including Arand nitrogen used in the sputtering method for forming the thin film,the internal stress of the thin film can be controlled without changingthe preferred orientation property of the thin film.

[0016] Therefore, in the case in which the thin film is mounted on, forexample, the piezoelectric resonator, even when the internal stress ofthe thin film is selected so as to decrease warping and cracking, theeffect on the resonance characteristics due to the change in thepreferred orientation property of the thin film is minimized.

[0017] Other features, elements, characteristics and advantages of thepresent invention will become apparent from the following detailedexplanations of preferred embodiments of the present invention withreference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a sectional schematic diagram of an AlN piezoelectricthin film according to a preferred embodiment of the present invention;

[0019]FIG. 2 is a graph showing the dependency of the internal stress ofthe AlN piezoelectric thin film on the nitrogen flow rate ratio;

[0020]FIG. 3 is a graph showing dependency of the C axis preferredorientation of the AlN piezoelectric thin film on the nitrogen flow rateratio;

[0021]FIG. 4 is a sectional schematic diagram of an AlN piezoelectricthin film resonator according to a preferred embodiment of the presentinvention;

[0022]FIG. 5 is a sectional schematic diagram of an example of aconventional piezoelectric thin film resonator; and

[0023]FIG. 6 is a sectional schematic diagram of another example of aconventional piezoelectric thin film resonator.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0024]FIG. 1 is a sectional schematic diagram of an AlN piezoelectricthin film according to a preferred embodiment of the present invention.An AlN piezoelectric thin film 10 as shown in FIG. 1 is formed on asubstrate 12 that is preferably made of, for example, Si or othersuitable material. In this case, the AlN piezoelectric thin film 10 isformed preferably using an RF magnetron sputtering apparatus includingan Al target and using a mixed gas including Ar and nitrogen. In oneexample of the present preferred embodiment, the AlN piezoelectric thinfilm 10 is formed at a temperature of the substrate 12 of approximately100° C., with an RF power of the apparatus of 100 W, and at a nitrogenflow rate ratio of about 5% to about 90%.

[0025] The dependency of the internal stress and the C axis preferredorientation of the AlN piezoelectric thin film 10, formed as describedabove, on the nitrogen flow rate ratio are shown in FIG. 2 and FIG. 3with graphs.

[0026] The internal stress σ was calculated from the relationshiprepresented by Formula 1 among the warp amount δ of the substrate 12before and after the formation of the AlN piezoelectric thin film 10,the measurement distance L of the warp amount, the film thickness d ofthe AlN piezoelectric thin film 10, the Young's modulus E of thesubstrate 12, the thickness t of the substrate 12, and the Poisson ratiop of the substrate 12.

σ=4Et ²δ/3d(1−p)L ²  Formula 1

[0027] Regarding the C axis preferred orientation, the half-width of the(002) rocking curve of the X-ray diffraction was measured.

[0028] As is clear from the graphs as shown in FIG. 2 and FIG. 3, at thenitrogen flow rate ratio of about 10% to about 75%, the internal stressof the AlN piezoelectric thin film 10 can be controlled within the rangeof about ±1 GPa, while the C axis preferred orientation of the AlNpiezoelectric thin film 10 is in a high, stable region of about 1.4° toabout 1.6°.

[0029] Therefore, in this AlN piezoelectric thin film 10, the internalstress can be controlled, while the C axis preferred orientation is kepthigh, by controlling the nitrogen flow rate ratio, which is a filmformation parameter.

[0030]FIG. 4 is a sectional schematic diagram of an AlN piezoelectricthin film resonator according to another preferred embodiment of thepresent invention. A piezoelectric thin film resonator 20 as shown inFIG. 4 includes an Si substrate 22.

[0031] On the Si substrate 22, a thin film 24 preferably made of SiO₂,Si₃N₄, or Al₂O₃, or other suitable material, a lower layer electrode 26a, an AlN piezoelectric material thin film 28 primarily including AlN asa piezoelectric thin film, and an upper layer electrode 26 b are formedin the aforementioned order. In this case, the thin film 24 ispreferably formed over the entire top surface of the Si substrate 22.The lower layer electrode 26 a is formed on a portion including thecentral portion on the top surface of the thin film 24. The AlNpiezoelectric thin film 28 is formed on the top surfaces of the thinfilm 24 and the lower layer electrode 26 a corresponding to the portionincluding the central portion of the thin film 24. The upper layerelectrode 26 b is formed on the top surface of the AlN piezoelectricthin film 28 corresponding to the portion including the central portionof the thin film 24. In this case, the AlN piezoelectric thin film 28 ispreferably formed under the conditions which are the same as thoseexisting when forming the AlN piezoelectric thin film 10 as shown in theaforementioned FIG. 1. Regarding the others, the thin film 24, the lowerlayer electrode 26 a, and the upper layer electrode 26 b are formedpreferably by sputtering, vapor deposition, or other suitable process.

[0032] A diaphragm 30 is formed on the substrate 22 by removing theportion thereof corresponding to the central portion of the thin film 24via anisotropic etching, RIE (Reactive Ion Etching), or other suitableprocess, from the reverse surface thereof.

[0033] In this piezoelectric thin film resonator 20, even when theinternal stress of the AlN piezoelectric thin film 28 is controlled torelax the stresses of Sio₂ having strong compressibility and Si₃N₄,Al₂O₃, or other suitable material, having strong tensile property, whichare used as the thin film 24, since the change in the preferredorientation property of the AlN piezoelectric thin film 28 is small,stable resonance characteristics, in which the electromechanicalcoupling coefficient k² is about 30% or more of the bulk, can beexhibited.

[0034] Furthermore, in this piezoelectric thin film resonator 20, thefilm thickness ratio of the thin film 24 relative to the AlNpiezoelectric thin film 28 may be adjusted to improve the resonancecharacteristics, such as the temperature characteristics of the resonantfrequency, although the adjustment of the warp of the diaphragm 30 dueto the change in the film thickness ratio can be controlled with theinternal stress of the AlN piezoelectric thin film 28.

[0035] Therefore, in this piezoelectric thin film resonator 20, evenwhen the internal stress of the AlN piezoelectric thin film 28 iscontrolled to minimize the warp of the diaphragm part 30, change in theresonance characteristics can be substantially eliminated.

[0036] The present invention can be applied to not only thepiezoelectric material thin films, but also to other thin films, such asdielectric material thin films and magnetic material thin films, andother thin films.

[0037] In addition, the present invention can be applied topiezoelectric thin film resonators as described above, but the presentinvention can also be applied to other electronic components, such asfilters, sensors, and actuators.

[0038] According to the present invention, the internal stress can becontrolled while the preferred orientation property is kept high in thethin films, for example, the piezoelectric material thin films, used forthe electronic components, for example, the piezoelectric thin filmresonators.

[0039] While the present invention has been particularly shown anddescribed with reference to preferred embodiments thereof, it will beunderstood by those skilled in the art that the foregoing and otherchanges in form and details can be made without departing from thespirit and scope of the invention.

What is claimed is:
 1. A thin film comprising: an AlN material providedon a surface of a substrate, wherein the crystallinity is the C axispreferred orientation, the half-width of a rocking curve is about 1.4°to about 1.6°, and an internal stress is within the range ofapproximately ±1 GPa.
 2. The thin film according to claim 1, wherein thethin film is one of a piezoelectric thin film, a dielectric thin filmand a magnetic material thin film.
 3. An electronic componentcomprising: a substrate; and a thin film disposed on the substrate andmade of an AlN material, wherein the crystallinity is the C axispreferred orientation, the half-width of a rocking curve is about 1.4°to about 1.6°, and an internal stress is within the range ofapproximately ±1 GPa.
 4. The electronic component according to claim 3,wherein the substrate is made of Si.
 5. The electronic componentaccording to claim 3, further comprising a thin film made of one SiO₂,Si₃N₄, and Al₂O₃, a lower layer electrode , the thin film, and an upperlayer electrode arranged in this order.
 6. The electronic componentaccording to claim 3, wherein a diaphragm is provided on the substrate.7. The electronic component according to claim 3, wherein the electroniccomponent is one of a piezoelectric thin film resonator, a filter, asensor, and an actuator.
 8. A method for manufacturing a thin filmcomprising the steps of: providing a substrate; and forming a thin filmon the substrate using a mixed gas of Ar and nitrogen such that the thinfilm includes an AlN material, wherein the crystallinity is the C axispreferred orientation, the half-width of a rocking curve is about 1.4°to about 1.6°, and an internal stress is within the range ofapproximately ±1 GPa; wherein said mixed gas has a nitrogen flow rateratio of about 10% to about 75%, wherein the nitrogen flow rate is aratio of a nitrogen flow rate relative to the sum of an Ar flow rate andthe nitrogen flow rate.
 9. The method according to claim 8, wherein thethin film is formed via a sputtering process.
 10. The method accordingto claim 8, wherein the thin the AlN piezoelectric thin film is formedat a temperature of the substrate of approximately 100° C., with an RFpower of about 100 W, and at a nitrogen flow rate ratio of about 5% toabout 90%.
 11. The method according to claim 8, wherein the thin film isone of a piezoelectric thin film, a dielectric thin film and a magneticmaterial thin film.
 12. The method according to claim 8, wherein thesubstrate is made of Si.
 13. The method according to claim 8, furthercomprising the steps of forming a thin film made of one SiO₂, Si₃N₄, andAl₂O₃, a lower layer electrode, forming the thin film, and an upperlayer electrode arranged in this order.
 14. The method according toclaim 8, further comprising the step of forming a diaphragm on thesubstrate.
 15. An electronic component comprising a thin filmmanufactured according to the method of claim
 8. 16. The electroniccomponent according to claim 15, wherein the electronic component is oneof a piezoelectric thin film resonator, a filter, a sensor, and anactuator.